The present invention relates to an airless dispenser device such as an airless pump, i.e. a pump without any air intake, so that the substance to be dispensed never comes into contact with air until it is dispensed. Such an airless pump is used, in particular, for dispensing substances that are liable to deteriorate on coming into contact with air. Such substances can be pharmaceuticals or cosmetics.
Conventionally, that type of dispenser comprises a dispensing chamber of variable volume, which chamber is provided with an inlet equipped with an inlet valve, and is provided with an outlet equipped with an outlet valve. In order to vary the volume of the dispensing chamber, a piston is provided that is generally actuated by means of an actuator rod through which the substance is delivered from the chamber. That is a quite conventional design for an airless pump.
In order to avoid any possibility of the substance to be dispensed being deteriorated by coming into contact with air, it is preferable to fill the container under a vacuum, and to mount the dispenser device on the container while it is still under a vacuum. During the operation of mounting the dispenser on the container under vacuum conditions, the inside of the dispenser, and in particular the dispensing chamber, is also subjected to the vacuum. The air is evacuated from the dispensing chamber via the inlet valve whose valve member can be in the form of a ball, of a washer, or of a conical flange member, which valve member does not provide good airtightness during this operation of fixing the dispenser under a vacuum. The valve seat does not have a surface state that is good enough to guarantee good airtightness. Therefore, air is also evacuated from the dispensing chamber and a partial vacuum then prevails therein. It should be noted that, during this step of mounting the dispenser on the container, the dispenser head is not yet mounted on the actuator rod of the dispenser. When the vacuum is interrupted, once the dispenser has been fixed to the container, the container and the pump are once again subjected to atmospheric pressure, so that all of the empty spaces inside the container and also inside the dispensing chamber are suddenly filled with the substance contained in the container. The dispensing chamber is thus at least partially filled. A major drawback then occurs when the dispenser head is mounted on the actuator rod, since mounting the head causes the rod to be displaced, which in turn causes the piston to be displaced, thereby reducing the volume of the dispensing chamber which is at least partially filled with the substance. As a result, substance contained in the dispensing chamber is dispensed. Therefore, prior to the device being sold and being used for the first time, the actuator rod and the expulsion channel in the dispenser head are filled with substance. That substance is then naturally in contact with the outside air, and can thus deteriorate.
Attempts have been made to solve that problem of substance being dispensed while the dispenser head is being mounted. Some such attempts consist in inserting a gas into the chamber before the dispenser is returned to atmospheric pressure. However, such a method is very difficult to implement because of the small diameter of the internal channel in the actuator rod, since it is necessary simultaneously to push back the outlet valve member and to inject the gas into the chamber. Such a gas injection method is therefore very difficult to implement.
Document EP-0 753 353 discloses a dispenser whose inlet tube is formed with a stopper that closes it off. When it is used for the first time, the stopper is punched out by an extension to the actuator rod, which extension penetrates into the inlet tube. The stopper is integrally molded with the inlet tube, which complicates molding. In addition, once it has been punched out, the stopper is free to move inside the inlet tube, and there is therefore a risk that said stopper might hinder dispenser operation.